1. Field of the Invention
The present invention relates to a high speed connection admission controller based on traffic monitoring and a method thereof, in which connection admission control is carried out for a homogeneous traffic having equal cell loss factors and/or a heterogeneous traffic having different cell loss factors per classes by using a peak cell rate as a traffic parameter on the basis of traffic monitoring in a connection controller of an asynchronous transfer mode exchanger, so that it becomes possible to improve real time processing and to reduce error rate.
2. Description of Prior Art
In general, congestion of a computer communication network classification means occurs when a traffic is induced, the traffic having a capacity larger than that capable to be processed. Such a congestion occurs due to unexpected change of traffic flow or some trouble in the network.
Especially, in an ultra high speed communication network environment such as asynchronous transfer mode (ATM) having a very low error rate, cell loss due to overflow of buffer is the most typical reason of the error and the congestion in the ATM network may degrade fatally the service quality.
In order to minimize the bad influence of the congestion, various congestion control is performed, wherein a preventive congestion control scheme and a reactive congestion control scheme are adopted for the congestion control in the ATM network. The preventive congestion control scheme and the reactive congestion control scheme are applied at different time point. The preventive congestion control scheme is to control before possible traffic congestion by expecting traffic situation of a communication network, and reported appropriate for a high speed transfer protocol such as the ATM rather than the reactive congestion control scheme.
One of the most typical one of the protective congestion control scheme is connection admission control (CAC) scheme and the CAC scheme is an operation which is carried out by a communication network for control virtual channel connection (VCC) or virtual path connection (VPC) in the procedure of call connection.
The CAC scheme has an object to prevent degradation of service quality of previously connected calls and a traffic generated from a new call by determining connection of the new call when the new call is requested to be connected.
Therefore, the CAC scheme should be designed to be controlled in real time with a high link efficiency while keeping good service quality of traffics.
Further, the CAC scheme as described above is to control traffics when realizing an ATM of an exchange system which has been proposed for providing broadband-integrated service digital network (B-ISDN) service, so that the CAC scheme is installed in an exchange of a wire communication ATM as a control algorithm.
Recently, such a traffic control algorithm has been commercialized to be accommodated in the exchanges or the algorithm itself has been individually commercialized.
Among them, a CAC scheme based on computation of equivalent bandwidth and a CAC scheme based burst modelling are widespread.
According to the CAC scheme based on the equivalent bandwidth, when a new call is requested to be connected, the new call is determined to be connected in such a manner that after a bit rate generated in a multiplied connection is approximately modelled to obtain an equivalent bandwidth, the call is determined to be in excess of a remaining capacity or not.
The equivalent bandwidth means a minimum bandwidth satisfying a demand for service quality of a corresponding call and has a value which is larger than an average cell rate (ACR) and smaller than a peak cell rate (PCR).
The equivalent bandwidth is computed with a various method, in which a typical one performs the computation by using traffic characteristics regardless of a whole capacity of physical link to obtain equivalent bandwidths of each call so that an equivalent bandwidth for whole traffic is obtained on the basis of queuing analysis.
Referring to the below mentioned formula 1, an equivalent bandwidth of each cell having a cell loss rate demand threshold value is obtained by formula 1: ##EQU1##
wherein, .alpha.=-1n .epsilon., R.sub.F =PCR, .rho.=ACR:PCR, b=an average burst length, and x=buffer size. PA1 wherein, if it is estimated that Gaussian distribution is performed for aggregated traffics in view of efficiency of multiplication, a size of a whole bandwidth .sub.C is obtained by formula 3: ##EQU3## PA1 wherein, m.sub.i represents an average bit rate, and .sigma..sub.i.sup.2 represents a distribution.
In this case, a size C of a whole bandwidth demanded when n connections are multiplied is obtained by the below formula 2: ##EQU2##
The CAC scheme based on the burst modelling determines to connect or not the new call by using a peak bit rate (PBR) and an average bit rate (ABR), regardless of distribution of on/off intervals of a cell arrive processor.
When n virtual channel, in which PBR=R and ABR=.alpha., are multiplied, a probability that a number of burst in an on-state is to be k at any time point is obtained by formula 4: ##EQU4##
As above, it is estimated that a probability P(n,k) that a size of a bandwidth demanded when k virtual channel is multiplied in the link is kR.
In this case, if a determination for connection admission of the new call excesses a threshold availability of bandwidth which is being used by already connected calls, the connection admission of the new call is determined by formula 5: ##EQU5##
When a physical link bandwidth is C and the number of a whole connected calls including the new call is n, if a probability that a size of the whole bandwidth to be used by the calls including the new call after the new call is connected does not exceed 90% of the physical link bandwidth is reasonable, that is, if the probability is smaller than (1-.epsilon.), the connection of the new call is admitted.
However, the CAC scheme based on the conventional equivalent bandwidth computation has disadvantages that it is difficult to compute a precise equivalent bandwidth in advance, link using efficiency is noticeably reduced in case of a small traffic source number, and real time control is difficult to be realized due to the time period required for and precision of the whole equivalent bandwidth computation.
Furthermore, even though the CAC scheme based on the burst modelling is convenient rather than the CAC scheme based on the equivalent bandwidth, it has still disadvantages that the computation becomes complicated under the heterogeneous traffic environment and relationship between the burst traffic characteristics and the service quality is unclear.